Minimally invasive surgeries (such as endoscopic surgery) are performed via portals through which a variety of elongated instruments may be passed to gain access to an internal surgical site. Cannulas are often inserted into portals to provide a convenient passageway through which the various instruments may pass. When cannulas are inserted through portals formed in walls of the body, it is desirable that the ends of the cannulas (disposed within the body) remain as close as possible to internal surfaces of the walls such that the ends of the cannulas do not protrude very far into the body to avoid inadvertent contact with and damage to anatomical structures, such as organs or nerves, for example. More importantly, when medical instruments are inserted through the cannulas, it is desirable that the cannulas remain stable and do not easily back out of the walls to negatively affect the surgical procedure.
Accordingly, there is a need for cannulas that are used in minimally invasive procedures and that remain stable within the body yet very close to internal surfaces of the walls.